While this ruling was expected by analysts and lawmakers, it could complicate if not delay Theresa May’s 12-point plan of focusing on global trade.

In a landmark ruling that could set Britain’s tone for Brexit, the UK’s Supreme Court has ruled that Prime Minister Theresa May must get parliamentary approval before she charts the country out from the European Union.

Dismissing the government’s argument that could use her executive powers, aka her “royal prerogative” to invoke Article 50 of the EU’s Lisbon Treaty and thus trigger divorce proceeding with the EU, the country’s highest court also rejected the government’s arguments that the UK’s devolved assemblies in Scotland, Wales and Northern Ireland should give their assent before invoking Article 50.

“The referendum is of great political significance, but the Act of Parliament which established it did not say what should happen as a result,” said David Neuberger, President of the Supreme Court. “So any change in the law to give effect to the referendum must be made in the only way permitted by the UK constitution, namely by an Act of Parliament.”

May, who had earlier repeatedly said she intends to trigger Article 50 before the end of March, will now have to seek the consent of British lawmakers thus potentially delaying her timetable. However, the main opposition party has made it clear that it would not come in the way of her timetable.

Last week, May showed her negotiation cards and revealed a strategy of “hard Brexit”, which promises a clean break from the world’s largest trading bloc.

Reactions to the verdict include a slight rise in the value of the sterling but however it sunk to the day’s low when the news of Britain’s devolved assemblies did not have to give their assent to trigger Article 50.